A randomized controlled trial is proposed to study the effect, in a cohort of racially and ethnically diverse group of overweight and obese pregnant women, of an Intensive Lifestyle Intervention (ILI) compared to Usual Care (UC) on gestational weight gain (GWG), infant fatness, and mothers'post-delivery weight retention. Women in the ILI arm will receive intensive counseling during pregnancy and group counseling after delivery regarding behavior, nutrition, and physical activity change. Visits to counselors will be weekly and additional telephone and internet contacts will occur. The mothers'will be assessed at 14 and 36 weeks of pregnancy and at 12 weeks and 52 weeks post-delivery. The measurements will be anthropometry, whole body MRI, EchoMRI, and whole body plethysmography (BodPod). The infants'measurements will be anthropometry, whole body MRI, EchoMRI, and whole body plethysmography (PeaPod) for fatness 12 weeks and 52 weeks. Mothers and children will have cardio-metabolic risk factors measured in plasma. Data will be collected regarding mothers'dietary intake and physical activity (questionnaires and accelerometry) to assist in counseling. Other data to be collected include questionnaires on quality of life, socio-economic status. Careful record will be kept of expenses in providing the ILI, so that cost analysis of the intervention can be calculated. The study is powered on the primary outcome, fatness of the infants at birth. We require 180 participants to attain appropriate power. We will enroll 210 so as to allow for some dropouts along the way. Each mother will be followed during pregnancy and for a year post delivery. Each infant will be followed for a year after birth. We have the ability o continue to follow these participants if further funding is forthcoming, as they are all local to or hospital's catchment area and our own physicians. If aims are achieved, namely that both children and mothers profit from the intervention, there should be a paradigm shift in how overweight pregnant women are treated. At present, there is a dearth of behavioral advice and intervention relating to GWG and physical activity provided to these women. Positive results from our study would provide evidence for ILI preventative intervention. PUBLIC HEALTH RELEVANCE: The prevalence of overweight and obesity in reproductive age US women is extremely high. These women when pregnant tend to gain higher than the recommended GWG, produce disproportionally fat babies, and retain much of the GWG post-partum. It is unknown whether maintaining GWG within the new lOM guidelines will produce leaner babies who have less risk of becoming obese adults, and will lead to less retention of GWG in women. A trial demonstrating these outcomes could lead to public health recommendations.